WASHINGTON — U.S. astronauts will continue to fly to and from the international space station aboard Russian Soyuz spacecraft through the end of 2017, NASA announced Jan. 27.

NASA plans to reserve six Soyuz seats to cover round-trip transportation and related training for three astronauts during 2017, according to a sole-source procurement notice posted online. Also included in the pending Soyuz order, which will be NASA’s second in as many years, is emergency crew rescue services through the spring of 2018, NASA said.

The procurement notice did not say how much NASA would pay the Russian space agency, Roscosmos, for these services. NASA spokesman Trent Perrotto, reached by email Jan. 28, had no immediate comment about the price.

Senior NASA officials hinted late last year that another contract for Soyuz rides was probably inevitable because the crew taxis U.S. companies are working on under the agency’s Commercial Crew Program would likely not be ready to fly before NASA’s current contract with Roscosmos runs out.

In May 2013, NASA paid Russia $424 million for astronaut transportation to the station in 2016, and for emergency crew rescue services through June 2017. The total cost averaged out to roughly $70 million a seat.

NASA has lacked the ability to ferry astronauts to the space station since the space shuttle fleet was retired in 2011. Boeing Space Exploration of Houston, Sierra Nevada Space Systems of Louisville, Colo., and Space Exploration Technologies Corp. of Hawthorne, Calif., are working on crew-carrying spacecraft using money from NASA’s Commercial Crew Program. NASA wants at least one of those vehicles to fly astronauts to station starting in 2017.

In its online procurement note, NASA said the first crewed demonstration flight to station under the Commercial Crew Program was tentatively scheduled for the fall of 2017.

NASA plans to pay for astronaut transportation with task orders from a contracting vehicle dubbed the Commercial Crew Transportation Capability Contract, competition for which is ongoing, with an award scheduled for August or September.

This fourth major contract of the Commercial Crew Program will pay for development and certification of at least one industry-designed crewed transportation system, plus task orders for routine flights. A company must complete a crewed demonstration before it is eleigible for a task order.

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Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...